Transient vibration measurement of an ultrasonic motor using stroboscopic phase-shift interferometry

We propose a method to visualize transient vibration of an ultrasonic motor (USM). Since a mechanical time constant is much larger than an electrical time constant, a mechanical transient phenomenon is excited at the starting of the USM. A stroboscopic phase-shift interferometry is used to measure the small and high speed vibration. The Fizeau-type interferometer is realized with a multi-mode semiconductor laser diode and an optical isolator. A laser beam is irradiated stroboscopically. Irradiation time of the laser beam is much shorter than the vibration period of the USM. Since a short irradiation time of the laser beam reduces contrast of interferogram, the laser beam is irradiated periodically synchronized by a gate signal which drives/stops a USM stator. These vibrations are compared with each other. The method described in this paper is useful for the transient vibration measurement of the USM.